Clarification of water

ABSTRACT

Aqueous suspensions of inorganic particles are clarified by addition of a polyacrylamide.

United States Patent Hedrick et a1. 14 1 Jan. 25, 1972 [54]CLARIFICATION OF WATER 2,981,630 4/1961 Rowland ..210/54 2,995,5128/1961 Weidner et al.. [72] Inventors: Ross M. Hedrick, St. Louis, Mo.;David T. 2 713,497 9 1955 oldham Mowry, Yokohama, Japan 2,616,818 111952 Azorlosa ..117 155 [731 Assign: Company FOREIGN PATENTS 0RAPPLICATIONS [221 Dim-3,1969 163,501 6/1955 Australia ...210/54 [21]Appl.No.: 873,657 475,671 11/1937 Great Britain ..210/54 Related US.Application Data OTHER PUBLICATIONS [63] Continuation of Ser. N0.199,659, June 4, 1962, Pat. Weiser The "M Oxides? McGraw-Hill Book (30-,

No. 3,516,932, which is a continuation-in-part of Ser. New York,|9261Page5 571mm 1 No. 230,701, June 8, 1951, abandoned, Ruehrwein andWard, Mechanism of Clay Aggregation by Polyelectrolytes," Soil Science,Vol. 73, No. 6, June 1952, [52] pp. 485-492&p.419 51 Michaels,Aggregation of Suspensions by Polyelectrolytes," 53 industrial &Engineering Chemistry, Vol. 46, No. 7, July 1954, pp. 1,485-- 1,490 5References Cited Michaels and Morelos, Polyelectrolyte Adsorption byKaolinite," industrial & Engineering Chemistry, Vol. 47, No. UNITEDSTATES PATENTS 9, Sept. 1955, PP- 1,801- 1,809 2,552,775 5/1951 Fischeret al. ..252/8.5 285. 22 ff'fSJSYLff,[i,';lfi,i'" VOL pages 2,625,5291/1953 Hedrick et a1. .210/54 X 5253331 251322 hfivirfifir" ""ZifiiExam/"M41939 Rogers K d I D 2,740,522 4/1956 Aimone et 31.. 209/166632;? JSeph D y Neal E and Mm 2,980,610 4/1961 Ruehrwein ..210/583,128,249 4/1964 Pye et a1. ..210/53 3,130,167 4/1964 Green .252/181EXEMPLARY CLAIM 3,157,595 1 1/ 1964 Johnson et a1 ..210/54 Aqueoussuspensions of inorganic particles are clarified by ad- 2,351,259 6/1944Fuetterer .210/54 X dition of a polyacrylamide. 2,728,724 12/1955 Gloor..210/54 X 23 Claims, No Drawings CLARIFICATION OF WATER Thisapplication is a continuation of application, Ser. No. 199,659 filedJune 4, 1962, now US. Pat. No. 3,516,932, which application is acontinuation-in-part of application, Ser. No. 230,701 filed June 8, 1951and now abandoned.

BACKGROUND OF THE INVENTION The present invention relates to a methodfor clarification of water containing suspended matter employingsynthetic polyelectrolytes as a settling aid.

According to the present invention, clarification of water containingsuspended matter is effected by adding to such water a syntheticwater-soluble polyelectrolyte which is a linear polymer containing amidesubstituents. The polymer consists of carbon atoms joined by singlevalence linkages and contain amide nitrogen in substituents thereon.Particles suspended in water generally have a negative charge, althoughunder special conditions existing in some waters, positively chargedparticles may also be encountered. Clarification (including flocculationand/or settling of suspended particles) in such water according to thepresent invention is effected by the controlled addition thereto ofcertain water-soluble polyelectrolytes. The amount of polyelectrolyteadded should be such as to produce a concentration not in excess of 0.1percent by weight.

Water containing suspended particles which may be treated by the presentinvention may have its origin either in natural or artificial sources,including industrial and sanitary sources. Waters containing suspendedparticles of natural origin are usually surface waters, wherein theparticles are suspended soil particles (silt), although subsurfacewaters may also be treated according to the present invention. Waterhaving its origin in industrial process (including sanitary water)operations may contain many different varieties of suspended particles.These particles are generally the result of the particular industrial orsanitary operation concerned. Prior to discharging such industrial wastewaters into natural water courses it generally is desired that thesuspended matter be removed.

The present process may likewise be applied to water contained in stockor fish ponds, lakes or other natural or artificial bodies of watercontaining suspended solids. It may be applied to industrial watersupplies either in preparation therefor, during or after use and priorto disposal. It may be applied to sanitary water supplies either for theelimination of suspended solids prior to use for such purposes, or itmay be applied to such waters which have become contaminated withimpurities from any source.

Most naturally occurring waters contain an amount of simple electrolytes(sodium, potassium, ammonium, calcium, aluminum salts, etc.) in excessof that necessary for the initial aggregation (flocculation) of theultimate silt particles. This is likewise true of particles of suspendedmaterial in industrial or sanitary waters. The ultimate particles ofsilt or other materials are therefore naturally somewhat aggregated(flocculated) by reason of the presence of such electrolytes. However,the forces binding such ultimate particles together are not great andmoreover are not such as to generally effect either rapid flocculationor strong enough to prevent deflocculation.

The synthetic polyelectrolytes herein disclosed combine with the chargedparticles causing rapid flocculation and also reinforce the formedaggregates of particles causing a general tightening or bonding togetherof the initial aggregates and an increased rate of coagulation andsettling, thus forming a less turbid supernatant liquid.

The addition of the polyelectrolyte to the water suspension should bemade in such a fashion that the resulting aggregation of the particlestakes place uniformly throughout the body of water. In order to obtain auniform addition of the polyelectrolyte to the water-borne suspension itis generally desirable to prepare a relatively dilute stock solution ofthe water-soluble polyamide and then to add such solution to the body ofwater in the proportions indicated above. Clarification may take placeeither in the natural body of water or it may be caused to take place inhydraulic thickeners of known design.

The amount of polyelectrolyte added to water containing chargedparticles will depend in general upon the number of such particles andthe volume of water to be treated. It is desired, of course, to employsufficient polyelectrolyte so that flocculation will take place withoutcausing the fonnation of stable dispersion of the particles. In thepast, solutions of polyelectrolytes have been employed in concentrationabove 0.5 percent (U.S. Pat. No. 1,976,679) in order to form stableaqueous dispersions of a variety of finely divided substances.

The precipitating action of the polyelectrolytes may be employed in theapplication of loading or filling materials to textiles or paper inorder to obtain special effects. As an example, rosin size is oftenadded to paperpulp prior to the formation of the sheet and precipitatedin the aqueous pulp by aluminum sulfate (paper makers alum). Whileadmirably serving this purpose it is recognized that aluminum sulfate isobjectionable not only because of its actual corrosiveness upon metalsbut also because of its hardening effect on organic substances such ascellulose.

By adding polyelectrolyte to the paper machine beater,

- either prior to or after the addition of size or filler, completeprecipitation can be achieved without the use of alum. The resultingpaper is obtained thus substantially free of electrolytes and the whitewater is clear and free of suspended particles. In this connection adifficulty often encountered with alum when applying certain colors topaper, which difficulty is manifested by a weakening of the color, isalso avoided.

The following examples illustrate various water-soluble polymers and themethod of preparation:

Polyacrylamide Ten grams of acrylamide and 0.05 gram of potassiumpersulfate were dissolved in ml. of water and heated in an oven at 60 C.for 5 hours. Because of some hydrolysis the polymer contained someammonium salt and imide groups in addition to acrylamide units. Thesolution was diluted with 400 ml. of water for use.Acrylamide-Acrylonitrile Copolymer Ninety grams of acrylamide, 10 gramsof acrylonitrile, 0.2 gram of potassium persulfate and 0.1 gram ofsodium bisulfite were dissolved in 1 liter of 50 percent methyl alcoholand heated for 4 days at 60 C. The resultant precipitated polymer wasthen filtered, washed with methanol and dried. Two grams of thismaterial was dissolved in 98 ml. of water for evaluation.

The present polyelectrolytes may be used for flocculating and settling alarge variety of suspended solids and their use is of considerableadvantage where it is desired to avoid the presence of electrolytes suchas those furnished by alum and ferric chloride or sulfate.

Typical examples of clarification processes which may be carried outaccording to our invention are those connected with paper making, claytreatment processes. pigment preparation, etc., or in other words,processes in which suspended particles are to be recovered orprecipitated from large amounts of water.

For optimum beneficial results the molecular weight of the polymer is ofsome importance. It appears that molecular weights should be in excessof 5,000 and preferably in excess of about 15,000. Molecular weight maydesirably be within the range of from 30,000 to 100,000 and even higher.The molecular weights should, however, not be so high as to yieldinsoluble polymers.

EXAMPLE 1 A solution containing 0.1 g. of polyacrylamide was added to 3liters of turbid river water containing suspended silt and having a pHof 8.05 and then 0.13 g. of aluminum sulfate added as a solution. Theresulting solution was stirred for 20 minutes and then allowed tosettle. A fast settling floc was obtained. Alum alone gave a slowsettling floc. The same amount of polyacrylamide added after the alumalso improved the rate of settling of the floc.

EXAMPLE 2 A solution containing 0.13 g. of Ferrisul" (ferric sulfate)was added to 3 liters of turbid river water. This was sufficient forflocculation. A much faster settling floc was obtained when the"Ferrisul" was followed with a solution of 0.1 g. of polyacrylamide.

EXAMPLE 3 To about 100 g. of Miami silt loam suspended in 1 liter of tapwater was added 0.1 g. of polyacrylamide in 5 cc. of water. The soilimmediately formed into flocs and settled out. This settling action wasnot impaired by the presence of 5 g. of sodium chloride, 5 g. of ferricchloride or 5 g. of aluminum sulfate.

As shown in these examples, inorganic electrolytes may be added beforeor after the treatment of the suspension with the polyamides. if theinitial aggregation by electrolytes in the aqueous suspension isadequate, the addition of electrolyte is not essential to a practicableprocess. If very pure water and even the surface water in some areas areused, the desirable inorganic electrolyte may be deficient. Under suchcircumstances the addition of the inorganic salts will serve a usefulpurpose.

The details of the invention as described above are not intended to belimitations on the scope of the invention except to the extent definedin the attached claims.

What is claimed is:

l. the method of treating a stable suspension of inorganic particles inan aqueous medium, which comprises adding to said medium anwater-soluble polyacrylamide having a molecular weight of at least 5,000in an amount sufficient to flocculate the suspended particles.

2. The method of claim 1 in which the amount is sufficient to flocculateand precipitate the suspended particles.

3. The method of claim 1 in which the suspension is of clay particles.

4. The method of claim 1 in which the polyacrylamide is in an amountsuch as to provide a concentration not in excess of 0. l percent byweight.

5. The method of treating a stable suspension of inorganic particles inan aqueous medium, which comprises adding to said medium a linearwater-soluble polymer of acrylamide having a molecular weight of atleast 5,000 in an amount sufficient to flocculate the suspendedparticles.

6. The method of claim 5 in which the amount is sufficient to flocculateand precipitate the suspended particles.

7. The method of claim 5 in which the suspension is of clay particles.

8. The method of clarifying water containing solid inorganic particlesin stable suspension, which comprises adding to said water a linearwater-soluble polymer of acrylamide having a molecular weight of atleast 5,000 in an amount sufficient to flocculate the suspendedparticles, and allowing the flocculated particles to settle.

9. The method of claim 8 in which the polymer is present in an amountnot exceeding 0.1 percent by weight.

10. The method of clarifying water containing solid inorganic particlesin stable suspension, which comprises adding to said water a linearwater-soluble polyacrylamide having a molecular weight of at least 5,000in an amount sufficient to flocculate the suspended particles.

11. The method of claim 10 in which the polymer is present in aconcentration not exceeding 01 percent by weight.

12. The method of clarifying a flocculated suspension of solid inorganicparticles in an aqueous medium which comprises adding sufficient polymerof acrylamide to further flocculate and to reinforce the bonds betweenthe flocculated particles but not in excess of 0.1 percent by weight andallowing the aggregates to settle.

13. The method of claim 12 in which the suspension is of clay.

14. A process of settling mineral suspensions containing finely dividedmineral solids which comprises treating said mineral suspensions with awater-soluble polymer of acrylamide having an average molecular weightof at least [0,000. said polymer being employed in an amount sufficientto flocculate the suspended mineral solids, and allowing the flocculatedmineral solids to settle.

15. The method of claim 1 further defined in that electrolytes selectedfrom the group consisting of alum, ferric chloride and ferric sulfateare not present.

16. The method of claim 1 further defined in that alum is not present.

17. The method of claim 1 in which the polyacrylamide combines withparticles of the suspension causing a bonding together into flocs and anincreased rate of settling.

18. The method of claim 15 in which the molecular weight is at least30,000.

19. The method of claim 15 in which the polymer of acrylamide hadundergone some hydrolysis prior to its addition to the suspension.

20. The method of treating a suspension of inorganic particles in anaqueous medium, which comprises adding to said medium a linearwater-soluble polymer of acrylamide having a molecular weight of atleast 5,000 in an amount such as to provide a concentration of polymersufficient to aggregate said particles but not in excess of0.l percentby weight.

21. The method of claim 20 in which the polyacrylamide contains someammonium salt and imide groups as well as acrylamide units.

22. The method of claim 20 in which the polymer is a copolymer ofacrylamide and acrylonitrile.

23. The method of treating a suspension of inorganic particles in anaqueous medium which comprises adding to said medium a linear polymerhaving as its repeating unit in an amount sufiicient to aggregate saidparticles but not in excess of 0.1 percent by weight thereby causing theparticles to aggregate and settle.

Disclaimer 3,637 ,491'.--Boss M. Hedm'clc, St. Louis, Mo., and David T.Mowa'y, Yokohama, J apan. CLARIFICATION OF WVATER. Patent dated J an.25, 1972. Disclaimer filed Sept. 20, 1971, by the assignee, MonsantoCompany.

Hereby disclaims the portion of the term of the patent subsequent toJune 22, 1987.

[Oyficial Gazette October 3, 1.972.]

2. The method of claim 1 in which the amount is sufficient to flocculateand precipitate the suspended particles.
 3. The method of claim 1 inwhich the suspension is of clay particles.
 4. The method of claim 1 inwhich the polyacrylamide is in an amount such as to provide aconcentration not in excess of 0.1 percent by weight.
 5. The method oftreating a stable suspension of inorganic particles in an aqueousmedium, which comprises adding to said medium a linear water-solublepolymer of acrylamide having a molecular weight of at least 5,000 in anamount sufficient to flocculate the suspended particles.
 6. The methodof claim 5 in which the amount is sufficient to flocculate andprecipitate the suspended particles.
 7. The method of claim 5 in whichthe suspension is of clay particles.
 8. The method of clarifying watercontaining solid inorganic particles in stable suspension, whichcomprises adding to said water a linear water-soluble polymer ofacrylamide having a molecular weight of at least 5,000 in an amountsufficient to flocculate the suspended particles, and allowing theflocculated particles to settle.
 9. The method of claim 8 in which thepolymer is present in an amount not exceeding 0.1 percent by weight. 10.The method of clarifying water containing solid inorganic particles instable suspension, which comprises adding to said water a linearwater-soluble polyacrylamide having a molecular weight of at least 5,000in an amount sufficient to flocculate the suspended particles.
 11. Themethod of claim 10 in which the polymer is present in a concentrationnot exceeding 0.1 percent by weight.
 12. The method of clarifying aflocculated suspension of solid inorganic particles in an aqueous mediumwhich comprises adding sufficient polymer of acrylamide to furtherflocculate and to reinforce the bonds between the flocculated particlesbut not in excess of 0.1 percent by weight and allowing the aggregatesto settle.
 13. The method of claim 12 in which the suspension is ofclay.
 14. A process of settling mineral suspensions containing finelydivided mineral solids which comprises treating said mineral suspensionswith a water-soluble polymer of acrylamide having an average molecularweight of at least 10,000, said polymer being employed in an amountsufficient to flocculate the suspended mineral solids, and allowing theflocculated mineral solids to settle.
 15. The method of claim 1 furtherdefined in that electrolytes selected from the group consisting of alum,ferric chloride and ferric sulfate are not present.
 16. The method ofclaim 1 further defined in that alum is not present.
 17. The method ofclaim 1 in which the polyacrylamide combines with particles of thesuspension causing a bonding together into flocs and an increased rateof settling.
 18. The method of claim 15 in which the molecular weight isat least 30,000.
 19. The method of claim 15 in which the polymer ofacrylamide had undergone some hydrolysis prior to its addition to thesuspension.
 20. The method of treating a suspension of inorganicparticles in an aqueous medium, which comprises adding to said medium alinear water-soluble polymer of acrylamide having a molecular weight ofat least 5,000 in an amount such as to provide a concentration ofpolymer sufficient to aggregate said particles but not in excess of 0.1percent by weight.
 21. The method of claim 20 in which thepolyacrylamide contains some ammonium salt and imide groups as well asacrylamide units.
 22. The method of claim 20 in which the polymer is acopolymer of acrylamide and acrylonitrile.
 23. The method of treating asuspension of inorganic particles in an aqueous medium which comprisesadding to said medium a linear polymer having as its repeating unit inan amount sufficient to aggregate said particles but not in excess of0.1 percent by wEight thereby causing the particles to aggregate andsettle.